forked from osmocom/wireshark
670 lines
30 KiB
Lua
670 lines
30 KiB
Lua
----------------------------------------
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-- script-name: proto.lua
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-- This is based on the dissector.lua example script, which is also used for testing.
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-- Unlike that one, this one is purely for testing even more things, notably
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-- the Proto/ProtoField API.
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----------------------------------------
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------------- general test helper funcs ------------
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local FRAME = "frame"
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local OTHER = "other"
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local total_tests = 0
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local function getTotal()
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return total_tests
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end
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local packet_counts = {}
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local function incPktCount(name)
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if not packet_counts[name] then
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packet_counts[name] = 1
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else
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packet_counts[name] = packet_counts[name] + 1
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end
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end
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local function getPktCount(name)
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return packet_counts[name] or 0
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end
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local passed = {}
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local function setPassed(name)
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if not passed[name] then
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passed[name] = 1
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else
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passed[name] = passed[name] + 1
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end
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total_tests = total_tests + 1
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end
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local fail_count = 0
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local function setFailed(name)
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fail_count = fail_count + 1
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total_tests = total_tests + 1
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end
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-- expected number of runs per type
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-- note ip only runs 3 times because it gets removed
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-- and bootp only runs twice because the filter makes it run
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-- once and then it gets replaced with a different one for the second time
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local taptests = { [FRAME]=4, [OTHER]=48 }
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local function getResults()
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print("\n-----------------------------\n")
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for k,v in pairs(taptests) do
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if v ~= 0 and passed[k] ~= v then
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print("Something didn't run or ran too much... tests failed!")
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print("Dissector type "..k.." expected: "..v..", but got: "..tostring(passed[k]))
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return false
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end
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end
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print("All tests passed!\n\n")
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return true
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end
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local function testing(type,...)
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print("---- Testing "..type.." ---- "..tostring(...).." for packet # "..getPktCount(type).." ----")
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end
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local function test(type,name, ...)
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io.stdout:write("test "..type.."-->"..name.."-"..getTotal().."-"..getPktCount(type).."...")
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if (...) == true then
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setPassed(type)
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io.stdout:write("passed\n")
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return true
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else
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setFailed(type)
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io.stdout:write("failed!\n")
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error(name.." test failed!")
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end
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end
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---------
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-- the following are so we can use pcall (which needs a function to call)
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local function callFunc(func,...)
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func(...)
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end
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local function callObjFuncGetter(vart,varn,tobj,name,...)
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vart[varn] = tobj[name](...)
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end
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local function setValue(tobj,name,value)
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tobj[name] = value
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end
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local function getValue(tobj,name)
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local foo = tobj[name]
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end
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------------- test script ------------
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----------------------------------
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-- modify original test function for now, kinda sorta
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local orig_test = test
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test = function (...)
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return orig_test(OTHER,...)
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end
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----------------------------------------
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-- creates a Proto object, but doesn't register it yet
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testing(OTHER,"Proto creation")
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test("Proto.__call", pcall(callFunc,Proto,"foo","Foo Protocol"))
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test("Proto.__call", pcall(callFunc,Proto,"foo1","Foo1 Protocol"))
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test("Proto.__call", not pcall(callFunc,Proto,"","Bar Protocol"))
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test("Proto.__call", not pcall(callFunc,Proto,nil,"Bar Protocol"))
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test("Proto.__call", not pcall(callFunc,Proto,"bar",""))
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test("Proto.__call", not pcall(callFunc,Proto,"bar",nil))
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local dns = Proto("mydns","MyDNS Protocol")
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test("Proto.__tostring", tostring(dns) == "Proto: MYDNS")
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----------------------------------------
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-- multiple ways to do the same thing: create a protocol field (but not register it yet)
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-- the abbreviation should always have "<myproto>." before the specific abbreviation, to avoid collisions
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testing(OTHER,"ProtoField creation")
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local pfields = {} -- a table to hold fields, so we can pass them back/forth through pcall()
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--- variable -- what dissector.lua did, so we almost match it
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local pf_trasaction_id = 1 -- ProtoField.new("Transaction ID", "mydns.trans_id", ftypes.UINT16)
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local pf_flags = 2 -- ProtoField.new("Flags", "mydns.flags", ftypes.UINT16, nil, base.HEX)
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local pf_num_questions = 3 -- ProtoField.uint16("mydns.num_questions", "Number of Questions")
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local pf_num_answers = 4 -- ProtoField.uint16("mydns.num_answers", "Number of Answer RRs")
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local pf_num_authority_rr = 5 -- ProtoField.uint16("mydns.num_authority_rr", "Number of Authority RRs")
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local pf_num_additional_rr = 6 -- ProtoField.uint16("mydns.num_additional_rr", "Number of Additional RRs")
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test("ProtoField.new",pcall(callObjFuncGetter, pfields,pf_trasaction_id, ProtoField,"new", "Transaction ID", "mydns.trans_id", ftypes.INT16,nil,"base.DEC"))
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test("ProtoField.new",pcall(callObjFuncGetter, pfields,pf_flags, ProtoField,"new", "Flags", "mydns.flags", ftypes.UINT16, nil, "base.HEX"))
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-- tries to register a field that already exists (from the real dns proto dissector) but with incompatible type
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test("ProtoField.new_duplicate_bad",not pcall(callObjFuncGetter, pfields,10, ProtoField,"new", "Flags", "dns.flags", ftypes.INT16, nil, "base.HEX"))
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test("ProtoField.int16_duplicate_bad",not pcall(callObjFuncGetter, pfields,10, ProtoField,"int16", "dns.id","Transaction ID"))
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-- now compatible (but different type)
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test("ProtoField.new_duplicate_ok",pcall(callObjFuncGetter, pfields,10, ProtoField,"new", "Flags", "dns.flags", ftypes.UINT32, nil, "base.HEX"))
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test("ProtoField.uint16_duplicate_ok",pcall(callObjFuncGetter, pfields,10, ProtoField,"uint16", "dns.id","Transaction ID"))
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-- invalid valuestring arg
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test("ProtoField.new_invalid_valuestring",not pcall(callObjFuncGetter, pfields,10, ProtoField,"new", "Transaction ID", "mydns.trans_id", ftypes.INT16,"howdy","base.DEC"))
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-- invalid ftype
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test("ProtoField.new_invalid_ftype",not pcall(callObjFuncGetter, pfields,10, ProtoField,"new", "Transaction ID", "mydns.trans_id", 9999))
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-- invalid description
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--test("ProtoField.new_invalid_description",not pcall(callObjFuncGetter, pfields,10, ProtoField,"new", "", "mydns.trans_id", ftypes.INT16))
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test("ProtoField.new_invalid_description",not pcall(callObjFuncGetter, pfields,10, ProtoField,"new", nil, "mydns.trans_id", ftypes.INT16))
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test("ProtoField.new_invalid_abbr",not pcall(callObjFuncGetter, pfields,10, ProtoField,"new", "trans id", "", ftypes.INT16))
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test("ProtoField.new_invalid_abbr",not pcall(callObjFuncGetter, pfields,10, ProtoField,"new", "trans id", nil, ftypes.INT16))
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test("ProtoField.int16",pcall(callObjFuncGetter, pfields,pf_num_questions, ProtoField,"int16", "mydns.num_questions", "Number of Questions"))
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test("ProtoField.int16",pcall(callObjFuncGetter, pfields,pf_num_answers, ProtoField,"int16", "mydns.num_answers", "Number of Answer RRs",base.DEC))
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test("ProtoField.int16",pcall(callObjFuncGetter, pfields,pf_num_authority_rr, ProtoField,"int16", "mydns.num_authority_rr", "Number of Authority RRs",base.DEC))
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test("ProtoField.int16",pcall(callObjFuncGetter, pfields,pf_num_additional_rr, ProtoField,"int16", "mydns.num_additional_rr", "Number of Additional RRs"))
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-- now undo the table thingy
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pf_trasaction_id = pfields[pf_trasaction_id]
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pf_flags = pfields[pf_flags]
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pf_num_questions = pfields[pf_num_questions]
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pf_num_answers = pfields[pf_num_answers]
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pf_num_authority_rr = pfields[pf_num_authority_rr]
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pf_num_additional_rr = pfields[pf_num_additional_rr]
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-- within the flags field, we want to parse/show the bits separately
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-- note the "base" argument becomes the size of the bitmask'ed field when ftypes.BOOLEAN is used
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-- the "mask" argument is which bits we want to use for this field (e.g., base=16 and mask=0x8000 means we want the top bit of a 16-bit field)
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-- again the following shows different ways of doing the same thing basically
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local pf_flag_response = ProtoField.new("Response", "mydns.flags.response", ftypes.BOOLEAN, {"this is a response","this is a query"}, 16, 0x8000, "is the message a response?")
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local pf_flag_opcode = ProtoField.new("Opcode", "mydns.flags.opcode", ftypes.UINT16, nil, base.DEC, 0x7800, "operation code")
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local pf_flag_authoritative = ProtoField.new("Authoritative", "mydns.flags.authoritative", ftypes.BOOLEAN, nil, 16, 0x0400, "is the response authoritative?")
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local pf_flag_truncated = ProtoField.bool("mydns.flags.truncated", "Truncated", 16, nil, 0x0200, "is the message truncated?")
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local pf_flag_recursion_desired = ProtoField.bool("mydns.flags.recursion_desired", "Recursion desired", 16, {"yes","no"}, 0x0100, "do the query recursivley?")
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local pf_flag_recursion_available = ProtoField.bool("mydns.flags.recursion_available", "Recursion available", 16, nil, 0x0080, "does the server support recursion?")
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local pf_flag_z = ProtoField.uint16("mydns.flags.z", "World War Z - Reserved for future use", base.HEX, nil, 0x0040, "when is it the future?")
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local pf_flag_authenticated = ProtoField.bool("mydns.flags.authenticated", "Authenticated", 16, {"yes","no"}, 0x0020, "did the server DNSSEC authenticate?")
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local pf_flag_checking_disabled = ProtoField.bool("mydns.flags.checking_disabled", "Checking disabled", 16, nil, 0x0010)
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-- no, these aren't all the DNS response codes - this is just an example
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local rcodes = {
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[0] = "No Error",
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[1] = "Format Error",
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[2] = "Server Failure",
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[3] = "Non-Existent Domain",
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[9] = "Server Not Authoritative for zone"
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}
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-- the above rcodes table is used in this next ProtoField
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local pf_flag_rcode = ProtoField.uint16("mydns.flags.rcode", "Response code", base.DEC, rcodes, 0x000F)
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local pf_query = ProtoField.new("Query", "mydns.query", ftypes.BYTES)
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local pf_query_name = ProtoField.new("Name", "mydns.query.name", ftypes.STRING)
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local pf_query_name_len = ProtoField.new("Name Length", "mydns.query.name.len", ftypes.UINT8)
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local pf_query_label_count = ProtoField.new("Label Count", "mydns.query.label.count", ftypes.UINT8)
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local rrtypes = { [1] = "A (IPv4 host address)", [2] = "NS (authoritative name server)", [28] = "AAAA (for geeks only)" }
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local pf_query_type = ProtoField.uint16("mydns.query.type", "Type", base.DEC, rrtypes)
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-- again, not all class types are listed here
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local classes = {
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[0] = "Reserved",
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[1] = "IN (Internet)",
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[2] = "The 1%",
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[5] = "First class",
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[6] = "Business class",
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[65535] = "Cattle class"
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}
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local pf_query_class = ProtoField.uint16("mydns.query.class", "Class", base.DEC, classes, nil, "keep it classy folks")
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testing(OTHER,"Proto functions")
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----------------------------------------
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-- this actually registers the ProtoFields above, into our new Protocol
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-- in a real script I wouldn't do it this way; I'd build a table of fields programaticaly
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-- and then set dns.fields to it, so as to avoid forgetting a field
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local myfields = { pf_trasaction_id, pf_flags,
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pf_num_questions, pf_num_answers, pf_num_authority_rr, pf_num_additional_rr,
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pf_flag_response, pf_flag_opcode, pf_flag_authoritative,
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pf_flag_truncated, pf_flag_recursion_desired, pf_flag_recursion_available,
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pf_flag_z, pf_flag_authenticated, pf_flag_checking_disabled, pf_flag_rcode,
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pf_query, pf_query_name, pf_query_name_len, pf_query_label_count, pf_query_type, pf_query_class }
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--dns.fields = myfields
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test("Proto.fields-set", pcall(setValue,dns,"fields",myfields))
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test("Proto.fields-get", pcall(getValue,dns,"fields"))
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test("Proto.fields-get", #dns.fields == #myfields)
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local pf_foo = ProtoField.uint16("myfoo.com", "Fooishly", base.DEC, rcodes, 0x000F)
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local foo = Proto("myfoo","MyFOO Protocol")
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local bar = Proto("mybar","MyBAR Protocol")
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test("Proto.fields-set", pcall(setValue,foo,"fields",pf_foo))
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test("Proto.fields-get", #foo.fields == 1)
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test("Proto.fields-get", foo.fields[1] == pf_foo)
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test("Proto.fields-set", not pcall(setValue,bar,"fields","howdy"))
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test("Proto.fields-set", not pcall(setValue,bar,"fields",nil))
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test("Proto.fields-get", #bar.fields == 0)
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test("Proto.name-get", foo.name == "MYFOO")
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test("Proto.name-set", not pcall(setValue,foo,"name","howdy"))
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test("Proto.description-get", foo.description == "MyFOO Protocol")
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test("Proto.description-set", not pcall(setValue,foo,"description","howdy"))
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test("Proto.prefs-get", typeof(foo.prefs) == "Prefs")
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test("Proto.prefs-set", not pcall(setValue,foo,"prefs","howdy"))
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local function dummy()
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setFailed(OTHER)
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error("dummy function called!")
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return
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end
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-- can't get this because we haven't set it yet
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test("Proto.dissector-get", not pcall(getValue,foo,"dissector"))
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-- now set it
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test("Proto.dissector-set", pcall(setValue,foo,"dissector",dummy))
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test("Proto.dissector-set", not pcall(setValue,foo,"dissector","howdy"))
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test("Proto.dissector-get", pcall(getValue,foo,"dissector"))
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test("Proto.prefs_changed-set", pcall(setValue,foo,"prefs_changed",dummy))
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test("Proto.prefs_changed-get", not pcall(getValue,foo,"prefs_changed"))
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test("Proto.prefs_changed-set", not pcall(setValue,foo,"prefs_changed","howdy"))
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local function dummy_init()
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--orig_test(OTHER,"Proto.init-called",true)
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return
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end
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test("Proto.init-set", pcall(setValue,foo,"init",dummy_init))
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test("Proto.init-set", pcall(setValue,bar,"init",dummy_init))
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test("Proto.init-get", not pcall(getValue,foo,"init"))
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test("Proto.init-set", not pcall(setValue,foo,"init","howdy"))
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local numinits = 0
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function dns.init()
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numinits = numinits + 1
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if numinits == 2 then
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getResults()
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end
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end
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----------------------------------------
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-- create some expert info fields
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local ef_query = ProtoExpert.new("mydns.query.expert", "DNS query message",
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expert.group.REQUEST_CODE, expert.severity.CHAT)
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local ef_response = ProtoExpert.new("mydns.response.expert", "DNS response message",
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expert.group.RESPONSE_CODE, expert.severity.CHAT)
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local ef_ultimate = ProtoExpert.new("mydns.response.ultimate.expert", "DNS answer to life, the universe, and everything",
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expert.group.COMMENTS_GROUP, expert.severity.NOTE)
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-- some error expert info's
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local ef_too_short = ProtoExpert.new("mydns.too_short.expert", "DNS message too short",
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expert.group.MALFORMED, expert.severity.ERROR)
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local ef_bad_query = ProtoExpert.new("mydns.query.missing.expert", "DNS query missing or malformed",
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expert.group.MALFORMED, expert.severity.WARN)
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-- register them
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dns.experts = { ef_query, ef_too_short, ef_bad_query, ef_response, ef_ultimate }
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----------------------------------------
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-- we don't just want to display our protocol's fields, we want to access the value of some of them too!
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-- There are several ways to do that. One is to just parse the buffer contents in Lua code to find
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-- the values. But since ProtoFields actually do the parsing for us, and can be retrieved using Field
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-- objects, it's kinda cool to do it that way. So let's create some Fields to extract the values.
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-- The following creates the Field objects, but they're not 'registered' until after this script is loaded.
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-- Also, these lines can't be before the 'dns.fields = ...' line above, because the Field.new() here is
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-- referencing fields we're creating, and they're not "created" until that line above.
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-- Furthermore, you cannot put these 'Field.new()' lines inside the dissector function.
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-- Before Wireshark version 1.11, you couldn't even do this concept (of using fields you just created).
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local questions_field = Field.new("mydns.num_questions")
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local query_type_field = Field.new("mydns.query.type")
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local query_class_field = Field.new("mydns.query.class")
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local response_field = Field.new("mydns.flags.response")
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-- here's a little helper function to access the response_field value later.
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-- Like any Field retrieval, you can't retrieve a field's value until its value has been
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-- set, which won't happen until we actually use our ProtoFields in TreeItem:add() calls.
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-- So this isResponse() function can't be used until after the pf_flag_response ProtoField
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-- has been used inside the dissector.
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-- Note that calling the Field object returns a FieldInfo object, and calling that
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-- returns the value of the field - in this case a boolean true/false, since we set the
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-- "mydns.flags.response" ProtoField to ftype.BOOLEAN way earlier when we created the
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-- pf_flag_response ProtoField. Clear as mud?
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--
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-- A shorter version of this function would be:
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-- local function isResponse() return response_field()() end
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-- but I though the below is easier to understand.
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local function isResponse()
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local response_fieldinfo = response_field()
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return response_fieldinfo()
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end
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----------------------------------------
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---- some constants for later use ----
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-- the DNS header size
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local DNS_HDR_LEN = 12
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-- the smallest possible DNS query field size
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-- has to be at least a label length octet, label character, label null terminator, 2-bytes type and 2-bytes class
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local MIN_QUERY_LEN = 7
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-- the UDP port number we want to associate with our protocol
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local MYDNS_PROTO_UDP_PORT = 65333
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----------------------------------------
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-- some forward "declarations" of helper functions we use in the dissector
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-- I don't usually use this trick, but it'll help reading/grok'ing this script I think
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-- if we don't focus on them.
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local byteArray2String, getQueryName
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----------------------------------------
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-- The following creates the callback function for the dissector.
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-- It's the same as doing "dns.dissector = function (tvbuf,pkt,root)"
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-- The 'tvbuf' is a Tvb object, 'pktinfo' is a Pinfo object, and 'root' is a TreeItem object.
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-- Whenever Wireshark dissects a packet that our Proto is hooked into, it will call
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-- this function and pass it these arguments for the packet it's dissecting.
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function dns.dissector(tvbuf,pktinfo,root)
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incPktCount(FRAME)
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-- We want to check that the packet size is rational during dissection, so let's get the length of the
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-- packet buffer (Tvb).
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-- Because DNS has no additonal payload data other than itself, and it rides on UDP without padding,
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-- we can use tvb:len() or tvb:reported_len() here; but I prefer tvb:reported_length_remaining() as it's safer.
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local pktlen = tvbuf:reported_length_remaining()
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-- We start by adding our protocol to the dissection display tree.
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-- A call to tree:add() returns the child created, so we can add more "under" it using that return value.
|
|
-- The second argument is how much of the buffer/packet this added tree item covers/represents - in this
|
|
-- case (DNS protocol) that's the remainder of the packet.
|
|
local tree = root:add(dns, tvbuf:range(0,pktlen))
|
|
|
|
-- now let's check it's not too short
|
|
if pktlen < DNS_HDR_LEN then
|
|
-- since we're going to add this protocol to a specific UDP port, we're going to
|
|
-- assume packets in this port are our protocol, so the packet being too short is an error
|
|
tree:add_expert_info(PI_MALFORMED, PI_ERROR, "packet too short")
|
|
return
|
|
end
|
|
|
|
-- Now let's add our transaction id under our dns protocol tree we just created.
|
|
-- The transaction id starts at offset 0, for 2 bytes length.
|
|
tree:add(pf_trasaction_id, tvbuf:range(0,2))
|
|
|
|
-- We'd like to put the transaction id number in the GUI row for this packet, in its
|
|
-- INFO column/cell. Firt we need the transaction id value, though. Since we just
|
|
-- dissected it with the previous code line, we could now get it using a Field's
|
|
-- FieldInfo extractor, but instead we'll get it directly from the TvbRange just
|
|
-- to show how to do that. We'll use Field/FieldInfo extractors later on...
|
|
local transid = tvbuf:range(0,2):uint()
|
|
pktinfo.cols.info:set("(".. transid ..")")
|
|
|
|
-- now let's add the flags, which are all in the packet bytes at offset 2 of length 2
|
|
-- instead of calling this again and again, let's just use a variable
|
|
local flagrange = tvbuf:range(2,2)
|
|
|
|
-- for our flags field, we want a sub-tree
|
|
local flag_tree = tree:add(pf_flags, flagrange)
|
|
-- I'm indenting this for calarity, because it's adding to the flag's child-tree
|
|
-- let's add the type of message (query vs. response)
|
|
local query_flag_tree = flag_tree:add(pf_flag_response, flagrange)
|
|
|
|
-- let's also add an expert info about it
|
|
if isResponse() then
|
|
query_flag_tree:add_proto_expert_info(ef_response, "It's a response!")
|
|
if transid == 42 then
|
|
tree:add_tvb_expert_info(ef_ultimate, tvbuf:range(0,2))
|
|
end
|
|
else
|
|
query_flag_tree:add_proto_expert_info(ef_query)
|
|
end
|
|
|
|
-- we now know if it's a response or query, so let's put that in the
|
|
-- GUI packet row, in the INFO column cell
|
|
-- this line of code uses a Lua trick for doing something similar to
|
|
-- the C/C++ 'test ? true : false' shorthand
|
|
pktinfo.cols.info:prepend(isResponse() and "Response " or "Query ")
|
|
|
|
flag_tree:add(pf_flag_opcode, flagrange)
|
|
|
|
if isResponse() then
|
|
flag_tree:add(pf_flag_authoritative, flagrange)
|
|
end
|
|
|
|
flag_tree:add(pf_flag_truncated, flagrange)
|
|
|
|
if isResponse() then
|
|
flag_tree:add(pf_flag_recursion_available, flagrange)
|
|
else
|
|
flag_tree:add(pf_flag_recursion_desired, flagrange)
|
|
end
|
|
|
|
flag_tree:add(pf_flag_z, flagrange)
|
|
|
|
if isResponse() then
|
|
flag_tree:add(pf_flag_authenticated, flagrange)
|
|
flag_tree:add(pf_flag_rcode, flagrange)
|
|
end
|
|
|
|
flag_tree:add(pf_flag_checking_disabled, flagrange)
|
|
|
|
-- now add more to the main mydns tree
|
|
tree:add(pf_num_questions, tvbuf:range(4,2))
|
|
tree:add(pf_num_answers, tvbuf:range(6,2))
|
|
-- another way to get a TvbRange is just to call the Tvb like this
|
|
tree:add(pf_num_authority_rr, tvbuf(8,2))
|
|
-- or if we're crazy, we can create a sub-TvbRange, from a sub-TvbRange of the TvbRange
|
|
tree:add(pf_num_additional_rr, tvbuf:range(10,2):range()())
|
|
|
|
local num_queries = questions_field()()
|
|
local pos = DNS_HDR_LEN
|
|
|
|
if num_queries > 0 then
|
|
-- let's create a sub-tree, using a plain text description (not a field from the packet)
|
|
local queries_tree = tree:add("Queries")
|
|
|
|
local pktlen_remaining = pktlen - pos
|
|
|
|
while num_queries > 0 and pktlen_remaining > 0 do
|
|
if pktlen_remaining < MIN_QUERY_LEN then
|
|
queries_tree:add_expert_info(PI_MALFORMED, PI_ERROR, "query field missing or too short")
|
|
return
|
|
end
|
|
|
|
-- we don't know how long this query field in total is, so we have to parse it first before
|
|
-- adding it to the tree, because we want to identify the correct bytes it covers
|
|
local label_count, name, name_len = getQueryName(tvbuf:range(pos,pktlen_remaining))
|
|
if not label_count then
|
|
q_tree:add_expert_info(PI_MALFORMED, PI_ERROR, name)
|
|
return
|
|
end
|
|
|
|
-- now add the first query to the 'Queries' child tree we just created
|
|
-- we're going to change the string generated by this later, after we figure out the subsequent fields.
|
|
-- the whole query field is the query name field length we just got, plus the 20byte type and 2-byte class
|
|
local q_tree = queries_tree:add(pf_query, tvbuf:range(pos, name_len + 4))
|
|
|
|
q_tree:add(pf_query_name, tvbuf:range(pos, name_len), name)
|
|
pos = pos + name_len
|
|
|
|
pktinfo.cols.info:append(" "..name)
|
|
|
|
-- the following tree items are generated by us, not encoded in the packet per se, so mark them as such
|
|
q_tree:add(pf_query_name_len, name_len):set_generated()
|
|
q_tree:add(pf_query_label_count, label_count):set_generated()
|
|
|
|
q_tree:add(pf_query_type, tvbuf:range(pos, 2))
|
|
q_tree:add(pf_query_class, tvbuf:range(pos + 2, 2))
|
|
pos = pos + 4
|
|
|
|
-- now change the query text
|
|
q_tree:set_text(name..": type "..query_type_field().display ..", class "..query_class_field().display)
|
|
|
|
pktlen_remaining = pktlen_remaining - (name_len + 4)
|
|
num_queries = num_queries - 1
|
|
end -- end of while loop
|
|
|
|
if num_queries > 0 then
|
|
-- we didn't process them all
|
|
queries_tree:add_expert_info(PI_MALFORMED, PI_ERROR, num_queries .. " query field(s) missing")
|
|
return
|
|
end
|
|
end
|
|
|
|
setPassed(FRAME)
|
|
|
|
-- tell wireshark how much of tvbuff we dissected
|
|
return pos
|
|
end
|
|
|
|
----------------------------------------
|
|
-- we want to have our protocol disseciton invoked for a specific UDP port,
|
|
-- so get the udp dissecotr table and add our protocol to it
|
|
local udp_encap_table = DissectorTable.get("udp.port")
|
|
udp_encap_table:add(MYDNS_PROTO_UDP_PORT, dns)
|
|
|
|
----------------------------------------
|
|
-- we also want to add the heuristic dissector, for any UDP protocol
|
|
-- first we need a heuristic dissection function
|
|
-- this is that function - when wireshark invokes this, it will pass in the same
|
|
-- things it passes in to the "dissector" function, but we only want to actually
|
|
-- dissect it if it's for us, and we need to return true if it's for us, or else false
|
|
-- figuring out if it's for us or not is not easy
|
|
-- we need to try as hard as possible, or else we'll think it's for us when it's
|
|
-- not and block other heuristic dissectors from getting their chanc
|
|
--
|
|
-- in practice, you'd never set a dissector like this to be heuristic, because there
|
|
-- just isn't enough information to safely detect if it's DNS or not
|
|
-- but I'm doing it to show how it would be done
|
|
--
|
|
-- Note: this heuristic stuff is new in 1.11.3
|
|
local function heur_dissect_dns(tvbuf,pktinfo,root)
|
|
|
|
if tvbuf:len() < DNS_HDR_LEN then
|
|
return false
|
|
end
|
|
|
|
local tvbr = tvbuf:range(0,DNS_HDR_LEN)
|
|
|
|
-- the first 2 bytes are tansaction id, which can be anything so no point in checking those
|
|
-- the next 2 bytes contain flags, a couple of which have some values we can check against
|
|
|
|
-- the opcode has to be 0, 1, 2, 4 or 5
|
|
-- the opcode field starts at bit offset 17 (in C-indexing), for 4 bits in length
|
|
local check = tvbr:bitfield(17,4)
|
|
if check == 3 or check > 5 then
|
|
return false
|
|
end
|
|
|
|
-- the rcode has to be 0-10, 16-22 (we're ignoring private use rcodes here)
|
|
-- the rcode field starts at bit offset 28 (in C-indexing), for 4 bits in length
|
|
check = tvbr:bitfield(28,4)
|
|
if check > 22 or (check > 10 and check < 16) then
|
|
return false
|
|
end
|
|
|
|
-- now let's verify the number of questions/answers are reasonable
|
|
check = tvbr:range(4,2):uint() -- num questions
|
|
if check > 100 then return false end
|
|
check = tvbr:range(6,2):uint() -- num answers
|
|
if check > 100 then return false end
|
|
check = tvbr:range(8,2):uint() -- num authority
|
|
if check > 100 then return false end
|
|
check = tvbr:range(10,2):uint() -- num additional
|
|
if check > 100 then return false end
|
|
|
|
-- don't do this line in your script - I'm just doing it so our testsuite can
|
|
-- verify this script
|
|
root:add("Heuristic dissector used"):set_generated()
|
|
|
|
-- ok, looks like it's ours, so go dissect it
|
|
-- note: calling the dissector directly like this is new in 1.11.3
|
|
-- also note that calling a Dissector objkect, as this does, means we don't
|
|
-- get back the return value of the dissector function we created previously
|
|
-- so it might be better to just call the function directly instead of doing
|
|
-- this, but this script is used for testing and this tests the call() function
|
|
dns.dissector(tvbuf,pktinfo,root)
|
|
|
|
-- since this is over a transport protocol, such as UDP, we can set the
|
|
-- conversation to make it sticky for our dissector, so that all future
|
|
-- packets to/from the same address:port pair will just call our dissector
|
|
-- function directly instead of this heuristic function
|
|
-- this is a new attribute of pinfo in 1.11.3
|
|
pktinfo.conversation = dns
|
|
|
|
return true
|
|
end
|
|
|
|
-- now register that heuristic dissector into the udp heuristic list
|
|
dns:register_heuristic("udp",heur_dissect_dns)
|
|
|
|
-- We're done!
|
|
-- our protocol (Proto) gets automatically registered after this script finishes loading
|
|
----------------------------------------
|
|
|
|
----------------------------------------
|
|
-- a helper function used later
|
|
-- note that it doesn't use "local" because it's already been declared as a local
|
|
-- variable way earlier in this script (as a form of forward declaration)
|
|
byteArray2String = function (barray, begin, length)
|
|
local word = {}
|
|
for i = 1, length do
|
|
word[i] = string.char(barray:get_index(begin))
|
|
begin = begin + 1
|
|
end
|
|
return table.concat(word)
|
|
end
|
|
|
|
----------------------------------------
|
|
-- DNS query names are not just null-terminated strings; they're actually a sequence of
|
|
-- 'labels', with a length octet before each one. So "foobar.com" is actually the
|
|
-- string "\06foobar\03com\00". We could create a ProtoField for label_length and label_name
|
|
-- or whatever, but since this is an example script I'll show how to do it in raw code.
|
|
-- This function is given the TvbRange object from the dissector() function, and needs to
|
|
-- parse it.
|
|
-- On success, it returns three things: the number of labels, the name string, and how
|
|
-- many bytes it covered of the buffer (which is always 2 more than the name length in this case).
|
|
-- On failure, it returns nil and the error message.
|
|
getQueryName = function (tvbr)
|
|
local label_count = 0
|
|
local name = ""
|
|
|
|
local len_remaining = tvbr:len()
|
|
if len_remaining < 2 then
|
|
-- it's too short
|
|
return nil, "invalid name"
|
|
end
|
|
|
|
local barray = tvbr:bytes() -- gets a ByteArray of the TvbRange
|
|
local pos = 0 -- unlike Lua, ByteArray uses 0-based indexing
|
|
|
|
-- get the first octet/label-length
|
|
local label_len = barray:get_index(pos)
|
|
if label_len == 0 then
|
|
return nil, "invalid initial label length of 0"
|
|
end
|
|
|
|
while label_len > 0 do
|
|
if label_len >= len_remaining then
|
|
return nil, "invalid label length of "..label_len
|
|
end
|
|
pos = pos + 1 -- move past label length octet
|
|
-- sadly, there's no current way to get a raw Lua string from a ByteArray (nor from Tvb for that matter)
|
|
-- so we need to do it one character at a a time
|
|
-- append the label and a dot to name string
|
|
name = name .. byteArray2String(barray, pos, label_len) .. "."
|
|
len_remaining = len_remaining - (label_len + 1) -- subtract label and its length octet
|
|
label_count = label_count + 1
|
|
pos = pos + label_len -- move past label
|
|
label_len = barray:get_index(pos)
|
|
end
|
|
|
|
-- we appended an extra dot, so get rid of it
|
|
name = name:sub(1, -2)
|
|
|
|
return label_count, name, name:len() + 2
|
|
end
|
|
|